/*
    Copyright 2005-2011 Intel Corporation.  All Rights Reserved.

    This file is part of Threading Building Blocks.

    Threading Building Blocks is free software; you can redistribute it
    and/or modify it under the terms of the GNU General Public License
    version 2 as published by the Free Software Foundation.

    Threading Building Blocks is distributed in the hope that it will be
    useful, but WITHOUT ANY WARRANTY; without even the implied warranty
    of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with Threading Building Blocks; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    As a special exception, you may use this file as part of a free software
    library without restriction.  Specifically, if other files instantiate
    templates or use macros or inline functions from this file, or you compile
    this file and link it with other files to produce an executable, this
    file does not by itself cause the resulting executable to be covered by
    the GNU General Public License.  This exception does not however
    invalidate any other reasons why the executable file might be covered by
    the GNU General Public License.
*/

/*
 * my_random_t.cpp:
 * An improved random number generation package.  In addition to the standard
 * rand()/srand() like interface, this package also has a special state info
 * interface.  The initstate() routine is called with a seed, an array of
 * bytes, and a count of how many bytes are being passed in; this array is then
 * initialized to contain information for random number generation with that
 * much state information.  Good sizes for the amount of state information are
 * 32, 64, 128, and 256 bytes.  The state can be switched by calling the
 * setstate() routine with the same array as was initiallized with initstate().
 * By default, the package runs with 128 bytes of state information and
 * generates far better random numbers than a linear congruential generator.
 * If the amount of state information is less than 32 bytes, a simple linear
 * congruential R.N.G. is used.
 * Internally, the state information is treated as an array of longs; the
 * zeroeth element of the array is the type of R.N.G. being used (small
 * integer); the remainder of the array is the state information for the
 * R.N.G.  Thus, 32 bytes of state information will give 7 longs worth of
 * state information, which will allow a degree seven polynomial.  (Note: the
 * zeroeth word of state information also has some other information stored
 * in it -- see setstate() for details).
 * The random number generation technique is a linear feedback shift register
 * approach, employing trinomials (since there are fewer terms to sum up that
 * way).  In this approach, the least significant bit of all the numbers in
 * the state table will act as a linear feedback shift register, and will have
 * period 2^deg - 1 (where deg is the degree of the polynomial being used,
 * assuming that the polynomial is irreducible and primitive).  The higher
 * order bits will have longer periods, since their values are also influenced
 * by pseudo-random carries out of the lower bits.  The total period of the
 * generator is approximately deg*(2**deg - 1); thus doubling the amount of
 * state information has a vast influence on the period of the generator.
 * Note: the deg*(2**deg - 1) is an approximation only good for large deg,
 * when the period of the shift register is the dominant factor.  With deg
 * equal to seven, the period is actually much longer than the 7*(2**7 - 1)
 * predicted by this formula.
 */

#include <dolphin/my_random.h>

#include <stdlib.h>
#ifndef _WIN32_WCE
#include <time.h>
#endif

/*
 * For each of the currently supported random number generators, we have a
 * break value on the amount of state information (you need at least this
 * many bytes of state info to support this random number generator), a degree
 * for the polynomial (actually a trinomial) that the R.N.G. is based on, and
 * the separation between the two lower order coefficients of the trinomial.
 */

#define     TYPE_0      0       /* linear congruential */
#define     BREAK_0     8
#define     DEG_0       0
#define     SEP_0       0

#define     TYPE_1      1       /* x**7 + x**3 + 1 */
#define     BREAK_1     32
#define     DEG_1       7
#define     SEP_1       3

#define     TYPE_2      2       /* x**15 + x + 1 */
#define     BREAK_2     64
#define     DEG_2       15
#define     SEP_2       1

#define     TYPE_3      3       /* x**31 + x**3 + 1 */
#define     BREAK_3     128
#define     DEG_3       31
#define     SEP_3       3

#define     TYPE_4      4       /* x**63 + x + 1 */
#define     BREAK_4     256
#define     DEG_4       63
#define     SEP_4       1

/*
 * Array versions of the above information to make code run faster -- relies
 * on fact that TYPE_i == i.
 */

#define MAX_TYPES   5L   /* max number of types above */

namespace dolphin {

static int my_degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
static int my_seps[MAX_TYPES]    = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };

/*
 * Initially, everything is set up as if from :
 *      initstate( 1, &randtbl, 128 );
 * Note that this initialization takes advantage of the fact that srandom()
 * advances the front and rear pointers 10*rand_deg times, and hence the
 * rear pointer which starts at 0 will also end up at zero; thus the zeroeth
 * element of the state information, which contains info about the current
 * position of the rear pointer is just
 *  MAX_TYPES*(rptr - state) + TYPE_3 == TYPE_3.
 */

static unsigned long my_randtbl[DEG_3 + 1] = {
    TYPE_3,
    0x9a319039U, 0x32d9c024U, 0x9b663182U, 0x5da1f342U,
    0xde3b81e0U, 0xdf0a6fb5U, 0xf103bc02U, 0x48f340fbU,
    0x7449e56bU, 0xbeb1dbb0U, 0xab5c5918U, 0x946554fdU,
    0x8c2e680fU, 0xeb3d799fU, 0xb11ee0b7U, 0x2d436b86U,
    0xda672e2aU, 0x1588ca88U, 0xe369735dU, 0x904f35f7U,
    0xd7158fd6U, 0x6fa6f051U, 0x616e6b96U, 0xac94efdcU,
    0x36413f93U, 0xc622c298U, 0xf5a42ab8U, 0x8a88d77bU,
    0xf5ad9d0eU, 0x8999220bU, 0x27fb47b9U
};

/*
 * fptr and rptr are two pointers into the state info, a front and a rear
 * pointer.  These two pointers are always rand_sep places aparts, as they cycle
 * cyclically through the state information.  (Yes, this does mean we could get
 * away with just one pointer, but the code for random() is more efficient this
 * way).  The pointers are left positioned as they would be from the call
 *          initstate( 1, randtbl, 128 )
 * (The position of the rear pointer, rptr, is really 0 (as explained above
 * in the initialization of randtbl) because the state table pointer is set
 * to point to randtbl[1] (as explained below).
 */

static  long    *my_fptr        = (long *) &my_randtbl[SEP_3 + 1];
static  long    *my_rptr        = (long *) &my_randtbl[1];

/*
 * The following things are the pointer to the state information table,
 * the type of the current generator, the degree of the current polynomial
 * being used, and the separation between the two pointers.
 * Note that for efficiency of random(), we remember the first location of
 * the state information, not the zeroeth.  Hence it is valid to access
 * state[-1], which is used to store the type of the R.N.G.
 * Also, we remember the last location, since this is more efficient than
 * indexing every time to find the address of the last element to see if
 * the front and rear pointers have wrapped.
 */

static  long    *my_state       = (long *) &my_randtbl[1];
static  int     my_rand_type    = TYPE_3;
static  int     my_rand_deg     = DEG_3;
static  int     my_rand_sep     = SEP_3;
static  long    *my_end_ptr     = (long *) &my_randtbl[DEG_3 + 1];

/*
 * srandom:
 * Initialize the random number generator based on the given seed.  If the
 * type is the trivial no-state-information type, just remember the seed.
 * Otherwise, initializes state[] based on the given "seed" via a linear
 * congruential generator.  Then, the pointers are set to known locations
 * that are exactly rand_sep places apart.  Lastly, it cycles the state
 * information a given number of times to get rid of any initial dependencies
 * introduced by the L.C.R.N.G.
 * Note that the initialization of randtbl[] for default usage relies on
 * values produced by this routine.
 */

void my_random::_my_srand( int seed /* =timer_null_seed(0) */ )
{
    int i;

    if (seed == timer_null_seed) {
        time_t timer;
        time(&timer);
        seed = (int)timer;
    }

    if (my_rand_type == TYPE_0) {
        my_state[0] = seed;
    }
    else {
        my_state[0] = seed;
        for (i=1; i<my_rand_deg; i++) {
            my_state[i] = 1103515245 * my_state[i - 1] + 12345;
        }
        my_fptr = &my_state[my_rand_sep];
        my_rptr = &my_state[0];
        for (i=0; i<my_rand_deg * 10; i++)
            _my_rand();
    }
}

/*
 * my_random:
 * If we are using the trivial TYPE_0 R.N.G., just do the old linear
 * congruential bit.  Otherwise, we do our fancy trinomial stuff, which is the
 * same in all ther other cases due to all the global variables that have been
 * set up.  The basic operation is to add the number at the rear pointer into
 * the one at the front pointer.  Then both pointers are advanced to the next
 * location cyclically in the table.  The value returned is the sum generated,
 * reduced to 31 bits by throwing away the "least random" low bit.
 * Note: the code takes advantage of the fact that both the front and
 * rear pointers can't wrap on the same call by not testing the rear
 * pointer if the front one has wrapped.
 * Returns a 31-bit random number.
 */

my_random::value_type my_random::_my_rand( void )
{
    value_type i;

    if (my_rand_type == TYPE_0) {
        i = my_state[0] = (my_state[0] * 1103515245 + 12345) & 0x7fffffff;
    }
    else {
        *my_fptr += *my_rptr;
        i = (*my_fptr >> 1) & 0x7fffffff; /* chucking least random bit */
        if (++my_fptr >= my_end_ptr) {
            my_fptr = my_state;
            ++my_rptr;
        }
        else {
            if (++my_rptr >= my_end_ptr)
                my_rptr = my_state;
        }
    }
    return i;
}

/*
 * initstate:
 * Initialize the state information in the given array of n bytes for
 * future random number generation.  Based on the number of bytes we
 * are given, and the break values for the different R.N.G.'s, we choose
 * the best (largest) one we can and set things up for it.  srandom() is
 * then called to initialize the state information.
 * Note that on return from srandom(), we set state[-1] to be the type
 * multiplexed with the current value of the rear pointer; this is so
 * successive calls to initstate() won't lose this information and will
 * be able to restart with setstate().
 * Note: the first thing we do is save the current state, if any, just like
 * setstate() so that it doesn't matter when initstate is called.
 * Returns a pointer to the old state.
 */

char * my_random::_my_initstate( unsigned seed, char *arg_state, int n )
{
    char *ostate = (char *)(&my_state[-1]);

    if (my_rand_type == TYPE_0)
        my_state[-1] = my_rand_type;
    else
        my_state[-1] = MAX_TYPES * (long)(my_rptr - my_state) + my_rand_type;
    if (n < BREAK_1) {
        if (n < BREAK_0)
            return 0;
        my_rand_type = TYPE_0;
        my_rand_deg = DEG_0;
        my_rand_sep = SEP_0;
    }
    else {
        if (n < BREAK_2) {
            my_rand_type = TYPE_1;
            my_rand_deg = DEG_1;
            my_rand_sep = SEP_1;
        }
        else {
            if (n < BREAK_3) {
                my_rand_type = TYPE_2;
                my_rand_deg = DEG_2;
                my_rand_sep = SEP_2;
            }
            else {
                if (n < BREAK_4) {
                    my_rand_type = TYPE_3;
                    my_rand_deg = DEG_3;
                    my_rand_sep = SEP_3;
                }
                else {
                    my_rand_type = TYPE_4;
                    my_rand_deg = DEG_4;
                    my_rand_sep = SEP_4;
                }
            }
        }
    }
    my_state = &(((long *)arg_state)[1]);   /* first location */
    my_end_ptr = &my_state[my_rand_deg];    /* must set end_ptr before srandom */
    _my_srand(seed);
    if (my_rand_type == TYPE_0)
        my_state[-1] = my_rand_type;
    else
        my_state[-1] = MAX_TYPES * (long)(my_rptr - my_state) + my_rand_type;
    return ostate;
}

/*
 * setstate:
 * Restore the state from the given state array.
 * Note: it is important that we also remember the locations of the pointers
 * in the current state information, and restore the locations of the pointers
 * from the old state information.  This is done by multiplexing the pointer
 * location into the zeroeth word of the state information.
 * Note that due to the order in which things are done, it is OK to call
 * setstate() with the same state as the current state.
 * Returns a pointer to the old state information.
 */

char * my_random::_my_setstate( char *arg_state )
{
    long *new_state = (long *)arg_state;
    int type = new_state[0] % MAX_TYPES;
    int rear = new_state[0] / MAX_TYPES;
    char *ostate = (char *)(&my_state[-1]);

    if (my_rand_type == TYPE_0)
        my_state[-1] = my_rand_type;
    else
        my_state[-1] = MAX_TYPES * (long)(my_rptr - my_state) + my_rand_type;
    switch (type) {
    case TYPE_0:
    case TYPE_1:
    case TYPE_2:
    case TYPE_3:
    case TYPE_4:
        my_rand_type = type;
        my_rand_deg = my_degrees[type];
        my_rand_sep = my_seps[type];
        break;
    }
    my_state = &new_state[1];
    if (my_rand_type != TYPE_0) {
        my_rptr = &my_state[rear];
        my_fptr = &my_state[(rear + my_rand_sep) % my_rand_deg];
    }
    my_end_ptr = &my_state[my_rand_deg]; /* set end_ptr too */
    return ostate;
}

}  // namespace dolphin
